The present invention relates to a drilling head for a rotary impact drill. Rotary impact drills are also known as hammer drills, center drills and core bits.
Impact drills are employed for drilling holes in rock or concrete by axially reciprocating the drill while rotating it such that a hardened cutting member at the end thereof fractures and pulverizes the rock before it. In order to prevent cushioning of the blow of the drill on the rock, it is desirable to remove the particles of rock from before the end of the drill. One way of accomplishing this is to provide an exhaust channel axially disposed in the shaft of a drill and a connection bore from the exhaust channel to a location near the cutting member.
One of the problems with exhaust channels is that their external openings tend to become clogged with larger particles of crushed rock. In addition, in order to prevent internal clogging, exhaust channels should not become narrower than their openings but instead should, if possible, effectively widen in order to prevent clogging at a constricted point.
Due to the requirement for a connecting bore from the exhaust channel to the vicinity of the cutting member, rotary impact drills of the prior art require larger diameter shafts than are desired. Otherwise, the strength of the drilling head is sufficiently impaired in the vicinity of the cutting member that it is not capable of absorbing impact forces arising during drilling.